Process for casting and waterproofing of elements cast in concrete, mortar, cement, by using a silicone resin

ABSTRACT

The process for simultaneously molding and rendering water-repellent molded components made of concrete, mortar, cement or the like consists, before pouring the concrete, cement or the like, in covering the interior of the mold with a composition comprising a resin which is a silicone copolymer in the absence of crosslinking agent of hydrolysable silane type and of curing catalyst in the composition. Molded component thus obtained and compositions for removing from the mold and rendering water-repellent.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR97/00432 filed on Mar. 12, 1997.

The present invention relates to a process for moulding and renderingwater-repellent building materials, such as moulded components made ofconcrete, mortar, cement or terracotta, for example tiles or bricks.Another subject-matter of the invention is the moulded objects thusobtained, as well as compositions for removing from the mould andrendering water-repellent.

Modern structures very often make use of moulded components made ofconcrete or mortar. These components can be moulded on site orprefabricated in specialized plants, with or without heating the item inan oven in order to accelerate its drying.

In order to facilitate removal from the mould and to minimize thedefects which these items can contain, the moulds generally have a washapplied to them comprising a substance called a mould-release agent.Good removal from the mould is particularly important because it avoidsthe cost of correcting the defects, a cost which can reach up to 15% ofthe cost of the building shell. The mould-release agents are generallymineral oils, whereas the moulds are generally made of steel, of wood orof plastic. Silicone resins are rarely used because of their high cost.

Once put in place, in particular when they constitute building facades,these items are generally protected from the damage caused by moisture(rain, mist, and the like) by a water-repellent treatment. Thisoperation of rendering water-repellent is expensive because of themanpower cost and the scaffolding cost.

Provision has already been made in the past for compositions given asfacilitating removal from the mould and, at the same time, renderingwater-repellent the items thus moulded. This relates to PatentApplication FR-A-2,231,488, which provides for the application, to thesurfaces of the moulds, of a mixture composed of water-repellent curableorganosilicon compounds, finely divided solid inorganic matter and,optionally, solvents. Repeating the examples of this application hasmade it possible to obtain satisfactory water-repellency of the mouldedproduct but has not made it possible to obtain good removal from themould, the surface of the moulded item exhibiting pits as well asnumerous off-white blemishes.

Patent Application FR-A-2,474,518 also discloses a composition based onsilicone resins which can be crosslinked at ambient temperature in thepresence of moisture, making it possible to obtain a non-stickwater-repellent film which is easy to detach and which is resistant tostaining. This composition can be used in a great many applications, forexample as coating agent for separation or removal from the mould or asagent for coating the surface of materials to be protected from thelight, from air, from water, and the like. It can be applied inparticular to cement, concrete, brick, tile and slate, as well as tostructures such as bridges and buildings. However, this document doesnot provide for simultaneously removing from the mould and renderingwater-repellent moulded building components.

In addition, as regards the application with which the present inventionis concerned, the composition according to this document cannot beapplied on a large scale for reasons of cost. This is because thiscomplex composition is composed of a mixture

a) of an organopolysiloxane resin,

b) of an α,ω-dihydroxydiorganopolysiloxane,

c) of a crosslinking agent based on an organosilane containinghydrolysable functional group(s) or its partial condensation and/orhydrolysis product, which is used to cure the composition at ambienttemperature.

In addition, a curing catalyst can also be provided.

The object of the present invention is to provide a novel process whichmakes it possible simultaneously to removal from the mould and to renderwater-repellent moulded components made of concrete, mortar, cement andthe like, which makes it possible both faultlessly to remove the mouldedcomponents from the mould and to render them water-repellent underconditions which are entirely satisfactory, while observing the economiccriteria which have to be observed in this type of activity.

More specifically, the object of the invention is to render economicallyacceptable the use of silicone resins for removing building componentsfrom the mould by providing a simple composition which provides fullyfor both removal from the mould and for rendering water-repellent.

These objects are achieved in accordance with the invention by a processbased very carefully on the ability of concrete, mortar, cement and thelike, by their alkaline nature, to themselves provide for the curing ofthe silicone resin according to the invention.

The subject-matter of the present invention is thus a process forsimultaneously moulding and rendering water-repellent moulded componentsmade of concrete, mortar, cement or the like, characterized in that,before pouring the concrete, mortar, cement or the like, the interior ofthe mould is covered with a composition comprising a resin which is asilicone copolymer of following formula (I):

 M_(α)D_(β)T_(γ)Q_(δ)(OR)_(ε)  (I)

where:

M=R¹R²R³SiO_(½)

D=R⁴R⁵SiO_(2/2)

T=R⁶SiO_(3/2)

Q=SiO_(4/2)

R¹, R², R³, R⁴, R⁵ and R⁶, which are identical to or different from oneanother, each represent a C₁-C₁₂ and more particularly a C₁-C₈hydrocarbon-comprising residue;

R is a hydrogen atom or a linear or branched C₁-C₄ alkyl radical;

the copolymer exhibits, in its structure, at least one T or Q unit;

the α, β, γ and δ symbols represent the molar fractions (or theproportion by number) of the silicon atoms respectively of M, D, T and Qtypes for one silicon atom; the ε symbol represents the molar fraction(or the proportion by number) of the ≡SiOR ends per silicon atom; thesesymbols varying within the following ranges:

α: 0-0.5

β: 0-0.95

γ: 0-0.9

δ: 0-0.8

ε: 0.05-2

with α+β+γ+δ=1

 in the absence of crosslinking agent of hydrolysable silane type and ofcuring catalyst in the composition.

The M units, when there are several of them, can be identical to ordifferent from one another; the same comment also applies to the D and Tunits.

According to a preferred embodiment of the invention, the resin is acopolymer of formula (I) where:

R¹ to R⁶, which are identical to or different from one another, eachrepresent a linear or branched C₁-C₈ alkyl radical;

the copolymer exhibits, in its structure, at least one T unit, the δsymbol then being a number other than zero;

at least 25% by number of one or more of the R¹ to R⁶ substituentsrepresent a linear or branched C₃-C₈ alkyl radical.

More preferably, the copolymer is of type:

D_(β)T_(γ)(OR)_(ε)

where:

R⁴ to R⁶, which are identical to or different from one another, eachrepresent a linear or branched C₁-C₈ alkyl radical;

at least 25% by number of one or more of the R⁴ to R⁶ substituentsrepresent a linear or branched C₃-C₈ alkyl radical;

β: 0.2-0.9

γ: 0.1-0.8

ε: 0.2-1.5.

More preferably still, the copolymer is of type:

D_(β)T_(γ)(OR)_(ε)

where:

R⁴ and R⁵, which are identical to or different from one another, eachrepresent a linear or branched C₁-C₂ alkyl radical;

R⁶, which are identical to or different from one another, each representa linear or branched C₃-C₈ alkyl radical;

R is a hydrogen atom or a linear C₁-C₃ alkyl radical;

β: 0.2-0.6

γ: 0.4-0.8

ε: 0.3-1.0.

Generally, each of the R¹ to R⁶ radicals can be a linear or branchedalkyl radical, for example methyl, ethyl, propyl, butyl or isobutyl; andalkenyl radical, such as, for example, vinyl; an aryl radical, forexample phenyl or naphthyl; an arylalkyl radical, such as, for example,benzyl or phenylethyl; an alkylaryl radical, such as, for example, tolylor xylyl; or an araryl radical, such as biphenylyl.

The silicone copolymer according to the invention is sufficient byitself to provide simultaneously for the faultless removal from themould of the moulded components and for rendering them water-repellent.It meets the objectives set out above and renders unnecessary asubsequent water-repellency treatment.

However, one or more surface-tension modifiers can be added to it inorder to improve, if need be, the spreading of the composition over themould and the cohesion between the resin and the concrete. The followingin particular can be added to it: one or more reactive or unreactivepolydiorganosiloxane oils, one or more other copolymers known per se,and/or one or more conventional mould-release agents.

α,ω-Trimethylsilyl polydimethylsiloxanes with a viscosity of between 10and 10,000 mPa.s, preferably between 50 and 5000 mPa.s, are highlysuitable as unreactive oils and α,ω-dihydroxylated polydimethylsiloxaneshaving the same viscosities as above are highly suitable as reactiveoils. These oils can be present in a proportion of 1 to 80%, inparticular 1 to 60%, preferably of 40 to 60%, by weight with respect tothe silicone resin (I)+oil combination.

Mention may in particular be made, as copolymers, of silicone-polyethercopolymers resulting from the reaction of a polyether of formula:

CH₂═CH—CH₂—[OCH₂CH₂]_(v)—[OCH₂CH(CH₃)]_(w)—OH

with a silicone oil of formula:

Me₃SiO(Me₂SiO)_(x)(MeHSiO)_(y)SiMe₃,

Me=methyl

with v and w other than 0 and in particular between 5 and 30

with x ranging from 20 to 150

with y ranging from 2 to 10.

The copolymer can have added to it an additive, such as a freepolyether, for example in a proportion by weight ranging from 40/60 to60/40, preferably of the order of 50/50.

These copolymers can be present in a proportion of 0.1 to 10%, inparticular of 0.5 to 5%, preferably of 0.5 to 2%, by weight with respectto the silicone resin (I)+copolymer combination.

It is also possible to add, to the resin, one or more conventionalmould-release agents which will make it possible to decrease the amountof resin and thus the cost while, of course, providing for themould-release criteria, the water-repellency furthermore still beingprovided for. These agents can be present in a proportion of 1 to 80%,in particular of 1 to 60%, preferably of 40 to 60%, by weight withrespect to the silicone resin (I)+conventional mould-release agentcombination.

The composition according to the invention is generally applied to themould in a proportion of 5 to 30 g/m², in particular of 15 to 25 g/m²,preferably of the order of 20 g/m².

The starting alkoxylated polyorganosiloxane resin can be obtained in away known per se by reacting haloalkylsilanes with one another (forexample cohydrolysis/alcoholysis of methyl- and propylchlorosilanes). Inpractice, the synthetic reaction mixture is aqueous. It comprisesalcohol, for example methanol in order to obtain R=methyl, ethanol inorder to obtain R=ethyl, and the like.

A further subject-matter of the present invention is the compositionsfor simultaneously removing from the mould and rendering water-repellentwhich comprise at least one resin which is a copolymer of formula (I) asdefined above and at least one surface-tension modifier, chosen inparticular form the group of reactive oils, unreactive oils, copolymersand mould-release agents described above.

It relates very particularly to a composition combining the resinsaccording to the invention with at least one mould-release agent.

The present invention will now be described in more detail usingembodiments given solely by way of non-limiting examples.

EXAMPLE 1 Method of Preparation of a DTOR Resin with R═CH₃

Reaction method: cohydrolysis/methanolysis of chlorosilanes.

32.62 mol of dimethyldichlorosilane and 32.62 mol ofpropyltrichlorosilane are charged to a 25 liter reactor. Amethanol/water mixture, i.e. 195.6 mol of methanol and 21.77 mol ofwater, is run in over 3 hours and 15 minutes with stirring. Thetemperature is maintained at 25° C. The mixture is brought to boilingpoint after the methanol/water mixture has been run in and is maintainedfor 4 hours and 30 minutes. The reaction mixture is subsequently allowedto separate by settling for one hour and the upper phase, whichrepresents approximately 6% of the resin, is removed. The residualchlorines are removed by readding methanol, successively 1.7, 1.5 and1.5 kg, removed by distillation. Neutralization is carried out with 0.23kg of sodium bicarbonate for half an hour at 40° C. 4.9 kg and 4.4 kgafter filtration are obtained.

This resin has a viscosity η at 25° C. of 27.9 mPa.s and the ²⁹Si NMRanalysis reveals the following distribution of the various units:

Units molar % D (OMe) 0.25 D (OMe)₂ 7.70 D 36.21 T (OMe)₃ 0.18 T (OMe)₂6.04 T (OMe) 26.51 T 23.11 MeOSi/Si = 0.548 mol/mol 100.00

Amount employed: 2728 g, i.e. 7.37 mol.

In the same way, the preparation is carried out of DTOR resins withR=linear C₁-C₈, in particular C₁-C₃, alkyl and more particularly C₂H₅,in accordance with the preferred embodiments of the invention. In orderto obtain R═C₂H₅, the preparation is carried out with ethanol instead ofmethanol.

EXAMPLE 2 Method of Preparation of a DT(OR) Resin with R═C₂H₅

Reaction method: cohydrolysis/methanolysis of chlorosilanes.

3.5 mol of dimethyldichlorosilane and 3.5 mol of propyltrichlorosilaneare charged to a 2 liter reactor. The temperature is brought to 60° C.and then an ethanol/water mixture (6.12 mol of ethanol/6.6 mol of water)is run in over 2 hours with stirring and heating to 80° C. The acidicethanol is subsequently removed by distillation at 120° C. for 1 h 50min.

The residual chlorines are subsequently removed by washing with 166 g ofethanol and 5.7 g of water (in order to adjust to the desired viscosity)and then distillation is carried out at 120° C. for 1 h 05 min. Themixture is cooled to 100° C. and neutralized with sodium bicarbonate(11.1 g) at 100° C. for 1 h. 515 g of resin are obtained after coolingto 50° C. and filtering.

This resin has a kinematic viscosity of 87.7 mm²/s at 25° C.

The ²⁹Si NMR analysis reveals the distribution given below of thevarious units:

Units Molar % relative to Si D (OR) 2.60 D 37.10 T (OR)₂ 5.80 T (OR)23.90 T 30.60

Number of Si(OR) units per Si atom=0.381

Formula of the DT(OR) resin:

D_(0.397)T_(0.603)(OR)_(0.381)

with D=(CH₃)₂SiO_(2/2) and T=C₃H₇SiO_(3/2)

This resin will be known as resin A in the continuation of thedescription.

EXAMPLE 3 Tests

1) Procedure for the preparation of the mortar

Equipment

Leroy-Somer kneader of the LS80L1 type used at its maximum speed.

Mould made of stainless steel with dimensions of 4×4×16 cm

Spatula

Brush

Products

450 g of Vicat CPA 50 cement

225 g of water

a bag of CEN standardized sand

Method

The moulds have a wash applied to them beforehand using the brush.

The cement is introduced into the bowl of the kneader, the water ispoured in and mixing is carried out immediately for 30 sec. The sand isadded and mixing is carried out for a further 1 min 30. The kneader ishalted for 1 min and then the kneading is resumed for 2 min. The mixtureis subsequently poured into the mould, packed down and levelled flatusing a spatula.

After drying for 24 hours in the mould, the test specimens are removedfrom the mould and dried for 8 days at 23° C. and 65% humidity.

2) Procedure for evaluating the water-repellent power

The water-repellent power of the various products is evaluated by awater uptake test by capillary attraction at 23° C. and an atmospherewith 65% humidity. The lower face of the concrete test specimens isplaced in water so that the lower surface is immersed in 3 mm of waterfor 8 days, after which the amount of water absorbed is determined byweighing.

3) Evaluation of the removal from the mould

The removal from the mould is evaluated by taking into account variousparameters, such as the ease of the removal from the mould (cohesiveforce of the mould with respect to the test specimen) or the appearanceof the test specimens: bubbles, blemishes.

A grade of between 0 and 10 (10=faultless removal from the mould: easy,and smooth and unblemished test specimen) is then given to each test.

4) Products tested

Test 1: untreated control

Tests 2 and 3: commercial mould-release agents, sold respectively underthe names Démoulux MSF® (Test 2) or Démoulux S3® (Test 3) by the companyCIA, France.

Tests 4 and 5: Examples 1 and 2 of Patent Application FR-A-2,231,488.

Tests according to the invention:

Test 6: resin A (prepared in Example 2)

Resin recorded as DTOR with R═C₂H₅;

Test 7: 50% resin A+50% oil B

Oil B: polydimethylsiloxane oil blocked at each of the ends of thechains by trimethylsiloxyl units having a viscosity of 300 mPa.s at 25°C. and having an {overscore (M)}_(n)=8300 (it comprises approximately110 dimethylsiloxyl units);

Test 8: 50% resin A+50% oil C

oil C: α,ω-dihydroxypolydimethylsiloxane having a viscosity of 3500mPa.s at 25° C., having an {overscore (M)}_(n)=26,150 (it comprisesapproximately 350 dimethylsiloxyl units) and containing 0.13% by weightof hydroxyl groups (i.e. 0.0076 SiOH units per 100 g of oil);

Test 9: 99% resin A+1% oil D

oil D=50/50 by weight mixture of a polymer containing silicone-polyetherblocks and of free polyether; the silicone-polyether polymer resultsfrom the reaction of a polyether of formula:

CH₂═CH—CH₂—[OCH₂CH₂]_(v)—[OCH₂CH(CH₃)]_(w)—OH

with a silicone oil of formula:

Me₃SiO(Me₂SiO)_(x)(MeHSiO)_(y)SiMe₃,

Me=methyl

with v=22 (ethylene oxide)

with w=24 (propylene oxide)

with x=73

with y=7.

5) Results

The results are collated in the table below.

Absorption of water after 8 Removal from the Test No. days mould/10 16.9% 5 2 6.7% 7 3 6.9% 9 4 1.46% 1 5 0.75% 0 6 0.67% 8 7 0.69% 8 8 0.63%7 9 0.95% 10

6) Conclusions

Commercial products (Tests 2 and 3) give satisfactory removal from themould but are entirely without water repellency.

The products claimed in Patent FR 2,231,488 (Tests 4 and 5) give goodwater-repellent properties but are very bad mould-release agents.

The products according to the invention (Tests 6 to 9) have good to verygood mould-releasing properties and an excellent water-repellent power.

EXAMPLE 4 Test

1) Procedure for preparation of the mortar

Equipment

Euromachine kneader of the M201 type used at a speed of 195 rev/min.

Mould made of stainless steel with dimensions of 40×25×5 cm

Products

900 g of Vicat CPA 50 cement

450 g of water

2 bags of CEN standardized sand

Method

The product is applied beforehand to the mould using a rag.

The cement is introduced into the bowl of the kneader, the water ispoured in and mixing is carried out immediately for 30 sec. The sand isadded and mixing is carried out for a further 1 min. The kneader ishalted for 1 min 30 and then the kneading is resumed for 1 min. Themixture is subsequently poured into the mould and vibrated for 2 min.

After drying for 24 hours in the mould, the slabs are removed from themould and are dried for 8 days exposed to the surrounding atmosphere.

2) Procedure for evaluating the water-repellent power

The water-repellent power of the various products is evaluated by awater uptake test with a Karsten tube, a test carried out according tothe directions of the RILEM standard No. II.4 of 1978 (RILEM=RéunionInternationale des Laboratoires d'Essais et de Recherches sur lesMatériaux et les Constructions [International Union of Laboratories forTests and Research on Materials and Structures]). The volume of waterabsorbed by the slab over a time of 4 hours is measured.

3) Evaluation of the removal from the mould

The removal from the mould is evaluated by taking into account variousparameters, such as the ease of the removal from the mould (cohesiveforce of the mould to the slab) or the appearance of the slabs: bubbles,blemishes.

A grade of between 0 and 10 (10=faultless removal from the mould: easy,and smooth and unblemished slab) is then given to each test.

4) Products tested

Test 1: untreated control.

Test 2: commercial mould-release agent sold under the name Estorob804-01® by the company Novance, France.

Tests according to the invention:

Test 3: resin A (prepared in Example 2) Resin recorded as DTOR withR═C₂H₅;

Test 4: 50% resin A+50% Estorob 804-01®.

5) Results

The results are collated in the table below.

Absorption of water after 4 Removal from the Test No. hours mould/10 1  5 ml 5 2   4 ml 9 3 0.05 ml 8 4 0.05 ml 9

6) Conclusions

The commercial product gives satisfactory removal from the mould butdoes not introduce a water-repellent property.

The products according to the invention (Tests 3 and 4) have goodmould-release properties as well as an excellent water-repellent power.

What is claimed is:
 1. A process for simultaneously moulding in a mould having an interior and rendering water-repellent moulded components made of concrete, mortar, or cement comprising the steps of: covering the interior of the mould before pouring the concrete, mortar, or cement, with a composition comprising a resin which is a silicone copolymer of following formula (I): M_(α)D_(β)T_(γ)Q_(δ)(OR)_(ε)  (I) wherein M=R¹R²R³SiO_(½) D=R⁴R⁵SiO_(2/2) T=R⁶SiO_(3/2) Q=SiO_(4/2) R¹, R², R³, R⁴, R⁵ and R⁶, which are identical to or different from one another, each represent a C₁-C₁₂ hydrocarbon-comprising residue; R is a hydrogen atom or a linear or branched C₁-C₄ alkyl radical; the α, β, γ and δ symbols represent the molar fractions (or the proportion by number) of the silicon atoms respectively of M, D, T and Q types for one silicon atom; the ε symbol represents the molar fraction (or the proportion by number) of the (−)₃SiOR ends per silicon atom; these symbols varying within the following ranges: α: 0-0.5 β: 0-0.95 γ: 0-0.9 δ: 0-0.8 ε: 0.05-2 with the proviso that α+β+γ+δ=1, and that the copolymer exhibits, in its structure, at least one T or Q unit; and in the absence of crosslinking agent of hydrolysable silane and of curing catalyst in the composition.
 2. A process according to claim 1, wherein the resin is a copolymer of formula (I) wherein: R¹ to R⁶, which are identical to or different from one another, each represents a linear or branched C₁-C₈ alkyl radical; with the proviso that the copolymer exhibits, in its structure, at least one T unit, the γ symbol then being a number other than zero; and at least 25% by number of one or more of the R¹ to R⁶ substituents represent a linear or branched C₃-C₈ alkyl radical.
 3. A process according to claim 1, wherein the copolymer is of formula: D_(β)T_(γ)(OR)_(ε) wherein: R⁴ to R⁶, which are identical to or different from one another, each represent a linear or branched C₁-C₈ alkyl radical; at least 25% by number of one or more of the R⁴ to R⁶ substituents represent a linear or branched C₃-C₈ alkyl radical; and β: 0.2-0.9 γ: 0.1-0.8 ε: 0.2-1.5.
 4. A process according to claim 1, wherein the copolymer is of formula: D_(β)T_(γ)(OR)_(ε) wherein: R⁴ and R⁵, which are identical to or different from one another, each represent a linear or branched C₁-C₂ alkyl radical; R⁶, which are identical to or different from one another, each represent a linear or branched C₃-C₈ alkyl radical; R is a hydrogen atom or a linear C₁-C₃ alkyl radical; and β: 0.2-0.6 γ: 0.4-0.8 ε: 0.3-1.0.
 5. A process according to claim 1, wherein the R¹ to R⁶ radicals are methyl, ethyl, propyl, butyl, isobutyl, vinyl, phenyl, naphthyl, benzyl, phenylethyl, tolyl, xylyl, or biphenylyl.
 6. A process according to claim 1, wherein the composition further comprises one or more surface-tension modifiers.
 7. A process according to claim 1, wherein the composition further comprises one or more reactive or unreactive polydiorganosiloxane oils.
 8. A process according to claim 7, wherein the oils are α,ω-trimethylsilyl polydimethylsiloxane oils with a viscosity of between 10 and 10,000 mPa.s.
 9. A process according to claim 7, wherein the oils are α,ω-dihydroxylated polydimethylsiloxane oils with a viscosity of between 10 and 10,000 mPa.s.
 10. A process according to claim 7, wherein the oils are present in a proportion of 1 to 80% by weight with respect to the weight of the silicone resin (I) and of the oil.
 11. A process according to claim 10, wherein the oils are present in a proportion of 1 to 60% by weight.
 12. A process according to claim 1, wherein the composition further comprises one or more silicone-polyether copolymers resulting from the reaction of a polyether of formula: CH₂═CH—CH₂—[OCH₂CH₂]_(v)—[OCH₂CH(CH₃)]_(w)—OH with a silicone oil of formula: Me₃SiO(Me₂SiO)_(x)(MeHSiO)_(y)SiMe₃, Me=methyl with v and w other than 0; with x ranging from 20 to 150; with y ranging from 2 to 10; and optionally in the presence of a free polyether additive.
 13. A process according to claim 12, wherein v and w are between 5 and
 30. 14. A process according to claim 13, wherein the copolymer is present in a proportion of 0.1 to 10% by weight with respect to the weight of the silicone resin (I) and of the copolymer.
 15. A process according to claim 14, wherein the copolymer is present in a proportion of 0.5 to 5% by weight.
 16. A process according to claim 1, wherein the composition further comprises one or more mould-release agents.
 17. A process according to claim 16, wherein the mould-release agent is present in a proportion of 1 to 80% by weight with respect to the weight of the silicone resin (I) and of the mould-release agent.
 18. A process according to claim 17, wherein the mould-release agent is present in a proportion of 1 to 60% by weight.
 19. A process according to claim 1, wherein the composition is applied to the mould in a proportion of 5 to 30 g/m².
 20. A process according to claim 19, wherein the composition is applied to the mould in a proportion of 15 to 25 g/m².
 21. A moulding and water-repellent composition, comprising at least one resin which is a silicone copolymer of formula (I): M_(α)T_(β)T_(γ)Q_(δ)(OR)_(ε)  (I) wherein: M=R¹R²R³SiO_(½) D=R⁴R⁵SiO_(2/2) T=R⁶SiO_(3/2) Q=SiO_(4/2); R¹, R², R³, R⁴, R⁵ and R⁶, which are identical to or different from one another, each represent a C₁-C₁₂ hydrocarbon-comprising residue; R is a hydrogen atom or a linear or branched C₁-C₄ alkyl radical; the α, β, γ and δ symbols represent the molar fractions (or the proportion by number) of the silicon atoms respectively of M, D, T and Q types for one silicon atom; the ε symbol represents the molar fraction (or the proportion by number) of the (−)₃ SiOR ends per silicon atom; these symbols varying within the following ranges: α: 0-0.5 β: 0-0.95 γ: 0-0.9 δ: 0-0.8 ε: 0.05-2 with the proviso that α+β+γ+δ=1, and that the copolymer exhibits, in its structure, at least one T or Q unit; and at least one surface-tension modifier selected from the group consisting of an unreactive oil, a reactive oil, a copolymer, and a mould-release agent in the absence of crosslinking agent of hydrolysable silane and of curing catalyst in the composition. 